myfile=open('text.txt')
i = 0
rep = 0
open = 0
ans = 1e9
first_close = 1e9
tot_close = 0
tot_open = 0
while(myfile):
    a = myfile.get()
    if (a!="{" and a!="}"):
        i+=1
        continue
    if (a=='{'):
        open+=1
        tot_open+=1
    else:
        first_close=min(first_close, i+1)
        if(open==0):
            rep+=1
        else:
            close+=1
            tot_close+=1
    if(open==1):
        ans=min(ans,i+1)
    if(open==0):
        ans=1e9
    i+=1
if(rep>1 or abs(tot_open-tot_close)>1):
    print(-1)
elif(tot_open-tot_close == 0 or (open>1) or (rep==1 and open>0)):
    print(-1)
else:
    if(tot_close>tot_open):
        print(first_close)
    else:
        print(ans)